Influence of Polystyrene Molecular Weight on Semiconductor Crystallization, Morphology, and Mobility

The morphological characteristics of organic semiconductors significantly impact their performance in many applications of organic electronics. A list of challenges such as dendritic crystal formation, thermal cracks, grain boundaries, and mobility variations must be addressed to optimize their efficiency and stability. This paper provides an in-depth overview of how different polymer additives (conjugated, semicrystalline, and amorphous polymers) influence the crystallization, morphology and mobility of some well-studied organic semiconductors. Conjugated polymers enhance molecular alignment and crystallinity, leading to distinct crystalline structures and improved charge transport properties. Semicrystalline polymers offer in-situ crystallization control, which improves film morphology and increases crystallinity and mobility. Amorphous polymers help minimize misalignment and promote parallel orientation of organic crystals, which is critical for effective charge transport. Special attention is given to polystyrene (PS) as a representative additive in this review, which highlights the significant effects of its molecular weight (Mw) on film morphology and charge transport properties. In particular, low-Mw PS (less than 20k) typically results in smaller, more uniform crystals, and enhances both charge transport and interface quality. Medium-Mw PS (20k to 250k) balances film stability and crystallinity, with moderate improvements in both crystal size and mobility. High-Mw PS (greater than 250k) promotes larger crystalline domains, better long-range order, and more pronounced improvement in charge transport, although it may introduce challenges such as increased phase separation and reduced solubility. This comprehensive analysis underscores the decisive role of polymer additives in optimizing the morphology of organic semiconductors and maximizing their charge transport for next-generation organic electronic applications.